The invention relates to a process and an arrangement which will enable an optimal polarization of shaped articles made from polymers. Shaped articles from polymers containing polar molecule groups in their primary structure, such as, f.i. polyvinylidene fluoride, polyvinyl fluoride, polyvinyl chloride, polyamide 11, 7, 55, or polyester, polyurethanes, polyurea, polyacrylonitrile, polycarbonates, are distinguished by piezoelectric and/or pyroelectric properties and nonlinear optical properties after having been treated by polarization in an electric field, and will, therefore, find an increasingly wide application as electroacoustic converters and also as temperature-measuring instruments. They are, f.i., used with success in microphones, loudspeakers, ultrasonic converters and for proving the presence of laser radiation.
A large number of descriptions of inventions and of publications have been devoted to the polarization of shaped articles from polymers (DE Letter of Disclosure No. 26 57 536, DE Letter of Disclosure No. 27 38 220, DE Letter of Disclosure No. 27 43 016; R. G. Kepler, R. A. Anderson: Ferroelectricity in polyvinylidene fluoride, J. Appl. Phys. 49 (1978) 3, p. 1232; M. H. Litt, G. Hsu, P. Basu: Pyroelectricity and piezoelectricity in nylon, 11. J. Appl. Phys. 48 (1977) 6, p. 2208). When polarizing shaped articles from polymers, it is essential to reach an optimal polarization with an expenditure that can be justified. It is of importance in this context to have strong electric fields (close to the puncturing field strength) act at increased temperatures on the shaped polymer article during the polarization process, without electrical punctures occurring therein.
In the descriptions of invention DE Letter of Disclosure No. 27 19 881, an arrangement and a process are described which are based upon the combined application of an electrical direct current field with an impulse-shaped electric field.
This method, and, respectively, the appropriate arrangement, have the disadvantage that, in the first place, they are of a complicated technical design (f.i. costly supply apparatus for the generation of voltage impulses, a complicated polarization arrangement) and, in the second place, they will generate only average pyroelectric coefficients. With the arrangement for the polarization of shaped polymer articles, as described in the DE Letter of Disclosure No. 27 19 881, polarization in strong electric fields requires an expensive technology with regard to apparatus. Three systems of apparatus are required for the generation of the polarizing voltage, wherein, f. i., the third apparatus system consists of two high-voltage sources and a complicated high-voltage proof control equipment. With another method (DE Letter of Disclosure No. 26 11 047, DE Publication of Specifications No. 26 11 047), it is already impossible in principle to polarize at high field strengths without causing the phenomena of punctures, and, apart from too limited a polarization, the relatively long polarizing times are of disadvantage. To overcome the disadvantages of the methods as known, it will be necessary to find a solution by which optimal polarization can be achieved within short times and by the use of simple technological means.